If you use Gmail you have a neat built in feature called “Undo Send”.   With this feature enable you have up to 10 seconds to hit a cancel button that appears after the message has been sent.   To enable Undo send you need to click on your Gmail “Settings” in the upper right of your webpage then choose the “Labs” tab and scroll down until you see the “Undo send” , then click on “Enable”, then either scroll to the top or bottom of the Labs page and click on the “Save Changes” Button.     You can now click on your “General Settings” and choose between 5 or 10 seconds for the delay, Don’t forget to hit “Save Changes” at the bottom of the page.   That’s it your done!    Now after you click send on an email and you realize oh no that was the wrong person or I really didn’t want to send that you have a chance to cancel it within 10 seconds.